1. Field of the Invention
This invention relates to a blower having a plurality of fans connected or engaged each other in a rotational axis direction.
2. Description of the Related Art
In order to improve a capacity of air flow and a static pressure generated by a fan without increasing its impeller's diameter, a blower called “a double fan” is widely used in which a plurality of axial fans are arranged along the rotational axis thereof.
In a conventional blower having a plurality of fan impellers, two or more impellers are encased in a single housing or each impeller is encased in each housing, and the housings are connected with each adjoining housing in rotational axis direction. Generally, a large amount of development cost is required to design a new blower including a design of its housing, therefore one way for realizing cost reduction is to connect or engage a plurality of existing axial fans or centrifugal fans in rotational axis direction, which meets a performance requested for the new blower.
There are two major ways to connect or engage two or more adjoining housings. One way is that flanges of the housings are fixedly coupled to each other by screws and the other is that elastic hooks formed on one housing are engaged with the recesses of the other housing.
In the case where the fans are fixedly connected by screws, however, special tool such as screwdriver or wrench may be required. This increases the number of steps for connecting the blowers as well as the number of parts of the blower, thereby the cost for producing the blower may increases because of its complex structure of the blower.
In connecting the adjoining fans by elastic hooks, on the other hand, since the elastic hooks can be formed at the same time as the housing is formed by a molding process, the cost for the housing with such elastic hooks may not increase. Also, the elastic hooks can be engaged very simply without increasing the number of steps for engaging.
However, when the connection by means of the elastic hooks is performed, there are two requirements contradicting each other. One requirement is for securing a sufficient elasticity caused by elastic deformation which may be required for completing the engaging step to make the two adjoining fans engage and the other requirement is for a sufficient engaging force. Specifically, in the case where the elasticity of the elastic hooks is increased to realize an easier engaging step, the engaging force decreases and the insufficient engaging force would be realized. On the other hand, in the case where the elasticity of the elastic hooks is decreased, the engaging force increases and the engaging step would not be accomplished, because the elastic hooks may be damaged or the housing may be warped.